/Engine/Source/Developer/BSPUtils/Public/BSPOps.h
Opt = Bsp optimization, BSP_Lame (fast), BSP_Good (medium), BSP_Optimal (slow) Balance = 0-100, 0=only worry about minimizing splits, 100=only balance tree.
static void bspBuild ( [UModel](API\Runtime\Engine\UModel) * Model, enum [EBspOptimization](API\Developer\BSPUtils\FBSPOps\EBspOptimization) Opt, int32 Balance, int32 PortalBias, int32 RebuildSimplePolys, int32 iNode )